Download the tip of the heart is

THE HEART
Location - in the mediastinum (the space between the lungs) - 2/3 to the left of the
midline
- the tip of the heart is called the apex - it points toward the left hip
- the flat end of the heart (where the large vessels emerge) is called the base
Pericardium - the sac surrounding the heart - consists of two portions
1. Fibrous Pericardium
- composes of fibrous connective tissue
- connects with heart at base of the great vessels
2. Serous Pericardium - double layered
(1) Parietal layer of the serous pericardium - fused to the inside of the
fibrous pericardium
(2) Visceral layer of the serous pericardium (epicardium) - attached to
the outside of the myocardium (heart muscle)
- between these layers is a film of serous fluid called pericardial fluid - reduces
friction
- inflammation of the pericardium is called pericarditis
The Heart Wall
- consists of three layers
1. Epicardium - the visceral layer of the serous pericardium
2. Myocardium- the cardiac muscle tissue
3. Endocardium - the endothelial lining inside of the heart - continuous with the
endothelium of the great vessels
Anatomy of the Heart
Chambers - two atrium (left and right) and two ventricles (left and right)
Great Vessels of the Heart
Superior vena cava - large vein that drains the body superior to the heart empties into the right atrium
Inferior vena cava - large vein that drains the body inferior to the heartempties into the right atrium
Coronary Sinus - drains the veins of the heart itself - empties into the right
atrium
Pulmonary Trunk - large artery that takes the unoxygenated blood from the
right ventricle to the lungs - divides into right and left pulmonary arteries
Pulmonary Veins - large veins (4) that bring oxygenated blood back from the lungs empty into the left atrium
Ascending Aorta - large artery that takes the oxygenated blood from the left
ventricle to the entire body and to the heart itself (via the coronary arteries)
Ligamentum arteriosum - was a duct connecting the pulmonary trunk to the
aorta (ductus arteriosus) that allowed blood to bypass the lungs in the fetus
ANTERIOR VIEW OF THE HEART AND ITS VESSELS
POSTERIOR VIEW OF THE HEART AND ITS VESSELS
INTERIOR VIEW OF THE HEART SHOWING VALVES AND CHAMBERS
1. Atrioventricular Valves
- between the atria and the ventricles
- the right AV valve is also called the tricusp because it has three cusps of
fibrous tissue
- the left AV valve is also called the bicusp because it has two cusps of
fibrous tissue, or the mitral valve because it looks like a bishops hat
- each AV valve has chordae tendineae attached to the pointed end of
the valve and anchored to a papillary muscle
2. Semilunar Valves
- between the ventricles and the major arteries
- the pulmonary semilunar valve lies between the right ventricle and the
pulmonary trunk
- the aortic semilunar valve lies between the left ventricle and the aorta
Conduction System
- spread of excitation (action potential) between cardiac muscle fibers is very
rapid due to the intercalated discs (gap junctions)
- the ANS innervates the heart but only increases or decreases the heart rate
but does not initiate contraction
- the conduction system of the heart allows the heart to beat continuously
without nervous innervation because the heart contains self-excitable cells
that spontaneously and rhythmically generate action potentials
Components of the Conduction System
1. The Sinoatrial Node (SA node)
- also known as the pacemaker
- located in the wall of the right atrium near the superior vena cava
- the muscle action potential initiated by the SA node spreads out to the atria
causing them to contract and at the same time depolarize the AV node.
2. The Atrioventricular Node (AV node)
- located in the interatrial septum
- last portion of the atria to be depolarized
- the muscle action potential initiated by the AV node travels by a tract called the
atrioventricular bundle (bundle of His) which connects with the left and right
bundle branches which connect with the ventricles via the conduction myofibrils causing the ventricles to contract
Note: impulse conduction through the conduction system generates electrical currents
that can be detected on the body surface. The recording of these currents is called an
electrocardiogram
ELECTROCARDIOGRAM (EEG)
- electrical activity of the conduction system of the heart recorded with an
electrocardiograph
- there are three types of ECG's (EKG's)
1. Resting
2. Stress
3. Ambulatory
Normal Record
- three waves appear
1. the P Wave - indicates atrial depolarization
2. the QRS Complex - indicates ventricular depolarization and atrial
repolarization
3. the T wave - indicates ventricular repolarization
- some readings and what they mean
- the P-Q (PR) interval - if lengthened represents damage to the wall of the atria
- the S-T Segment - is elevated in myocardial infarction
The Cardiac Cycle
- in a normal heartbeat the two atria contract together first (atrial systole) then relax
(diastole) as the ventricles contract (ventricular systole)
- a complete heartbeat consists of atrial and ventricular systole and diastole
- for a complete description of what occurs during a normal cardiac cycle read
page 605 and 606 of your text and study figure 20.9 on page 606.
Heart Sounds
- listening to heart sounds is called auscaltation
- the first sound has being described as sounding like lub and is produced by
the AV valves closing
- the second sound has being described as sounding like dub and is produced by
the semilunar valves closing
Autonomic Control of Heart rate
Cardioacceleratory Center
- in the medulla
- passes via cardioacceleratory nerves (sympathetic) to:
- the SA node
- the AV node
- the myocardium of the ventricles
- release NE which:
- increases heart rate
- increases force of contraction
- therefore increases cardiac output
Cardioinhibitory Center
- in the medulla
- passes via the vagus nerve (parasympathetic) to:
- the SA node
- the AV node
- release ACh which:
- decrease heart rate
- decrease force of contraction
- therefore decreases cardiac output